LOS ANGELES — A cold storm system will bring snow showers to Southern California through Thursday night and brought the snow level down to an unusually low 1,500 feet, National Weather Service forecasters said.

“This storm system will likely bring the lowest snow levels of the season, with snow levels locally falling to 1,500 feet or lower on Thursday,” said an NWS statement.

“… There is the potential for brief snow showers in some areas that rarely see snow, such as the higher valleys of Los Angeles and Ventura counties, foothills, and Santa Monica mountains. Many roads will be affected due to the very low elevation snow levels,” the statement warned.

Forecasters said they expect snow accumulations of 1 to 4 inches, with 4 to 6 inches possible across the eastern San Gabriel Mountains in L.A. County, along with “dangerous winter weather driving conditions due to snow showers, icy roadways, and gusty winds.”

Forecasters also urged motorists to be prepared for reduced visibility on some roadways, including Interstate 5 from The Grapevine to Santa Clarita and Highway 14, the Antelope Valley Freeway, through Soledad Canyon.

The weather service issued a winter weather advisory signifying horrendous travel conditions through 10 p.m. Thursday in the San Gabriel Mountains and the Antelope Valley, although drivers were able to travel on the Golden State Freeway over the Grapevine this morning with no restrictions, according to the California Highway Patrol.

“There are no restrictions on any freeways,” said CHP Officer Tony Polizzi.

Snow fell on portions of the 14 Freeway around 6 p.m. Wednesday but did not stick, although rain and hail were reported around 5:30 p.m. Wednesday, causing some vehicles to slide.

The snow level in the San Gabriels was at between 3,000 and 3,500 feet Wednesday night and expected to fall to 2,000 feet Thursday.

“Plan on slippery road conditions and be prepared for reduced visibility at times,” warned the NWS statement. “Portions of highways 14 and 138 (Pearblossom Highway), mainly near the foothill communities could be impacted by light snow and icy roads.”

In addition to prompting road closures and flooding, the storm forced a daylong closure of the Knott’s Berry Farm and Six Flags Magic Mountain theme parks Wednesday. It also delayed play at the Genesis Open golf tournament at Riviera Country Club, and it forced the cancellation of a Hollywood Walk of Fame ceremony for rock band Aerosmith.

Off the coast, thunderstorms are expected through Thursday night as a result of the moist and unstable air mass in the region.

“Any thunderstorm that forms will be capable of producing local gale force winds and rough seas, dangerous lightning, heavy rainfall with reduced visibility and waterspouts,” said an NWS statement.

Also in effect Thursday through Friday morning is a freeze watch. Temperatures are expected to drop to between 29 and 32 degrees Friday morning.

“A hard freeze can kill crops and sensitive vegetation and harm outdoor pets and livestock. Extended exposure to cold can cause hypothermia,” noted an NWS statement. “A freeze watch means temperatures between 29 and 32 degrees or less will be possible for at least two consecutive hours. Protective measures to save outdoor plants may be needed. Vulnerable animals and pets should be kept indoors in a house or barn.”

Forecasters said a cold system will move into the area Friday afternoon, likely dropping the snow level to about 4,000 feet but with far less likelihood of rain than Wednesday and Thursday.

The NWS forecast showers in L.A. County Thursday and highs of 35 on Mount Wilson; 44 in Palmdale and Lancaster; 50 in Santa Clarita; 52 in Avalon; 54 in West Covina, Pasadena, San Gabriel and Burbank; 55 in Northridge, North Hollywood, Van Nuys and Woodland Hills; 56 in downtown L.A., Whittier and at LAX; and 57 in Torrance and San Pedro. Sunny skies are forecast Friday and Saturday, followed by four partly cloudy days in the 60s.

A combination of showers and partly cloudy skies was forecast in Orange County Thursday, along with highs of 29 degrees on Santiago Peak; 44 on Ortega Highway at 2,600 feet; 50 in Fremont Canyon; 51 in Trabuco Canyon; 53 in Yorba Linda and San Clemente; 54 in Mission Viejo and Laguna Beach; 55 in Newport Beach; 56 in Anaheim; and 57 in Santa Ana, Fullerton and Irvine. Sunny skies and temperatures in the 50s and 60s are forecast through Tuesday followed by a partly cloudy day.